1864.) Farrparkn on Submarine Telegraph Cables. 627 
Tapun, showing the Conducting Power of certain Commercial Coppers. 
ul be 0 wit ° . . . oT . 
Conducting Tenney Cause of Diminution of Conducting 
Power. aoe Power. 
Centigrade, 
Quality of Copper. 
oO 
Pure copper . . . | 100: mean}| 15°5 
Specimen furnished 98°78 15°5 Traces of silver. No suboxide of 
by Mr. Tennant, copper. 
cut from a piece 
13 ton in weight 
American (Lake Su- 92°57 15: Traces of iron, silver (+03 per 
perior) cent.), and suboxide of copper. 
Australian (Burra 88°86 14° Traces of iron and suboxide of 
Burra) copper. 
Best selected. . . $1°35 14:2 Traces of iron, nickel, antimony, 
suboxide of copper, &e. 
Bright copper wire . 72°22 UBso"/ Traces of lead, iron, nickel, sub- 
oxide of copper, &e. 
Tough copper. . 71°03 a as) Traces of lead, iron, nickel, anti- 
mony, suboxide of copper, &e. 
Russian (Demidoff) 59°34 YAS Traces of iron, arsenic, nickel, 
suboxide of copper, &c. The 
arsenic present may be consi- 
dered the chief reason of the 
low conducting power. 
Spanish (Rio Tinto). 14°24 14:8 Two per cent. arsenic; traces of 
lead, iron, nickel, suboxide of 
copper, &e. The low conduct- 
ing power is to be attributed to 
the arsenic present. 
Gibraltar core :— 
Specimen, No. 112 90°7 15°5 ee of lead, suboxide of cop- 
SS al 89°5 1505} per, iron, and antimony. 
Traces of lead,arsenic (very small), 
2 7) . ) 
2 D ar Ln ae ; iron, nickel, antimony, and sub- 
4 ail a oxide of copper. 
From the above table, it would appear that the difference of con- 
ducting power in the different kinds of copper is caused by the impuri- 
ties contained in the specimens experimented upon. The Rio Tinto 
copper, in so far as regards its conducting power, being no better 
than iron. 
Tt has been found that there are no alloys of copper which have a 
better conducting power than the metal itself; but, as perfectly pure 
copper is not to be obtained, we have only to reiterate that copper, as 
pure as can be possibly procured, is the only metal which should be 
used for the conducting wire of a submarine cable. 
Insulation.—As copper seems to stand out prominently as the most 
fitting conductor, so does caoutchouc, or india-rubber, appear almost 
specially intended for the purpose of insulation. Its qualities, in this 
respect, are of the highest order. It is tough, highly elastic, of less 
Specific gravity than water, easily manipulated, extremely durable 
under water, nearly impervious to moisture, except superficially, and 
not excessively costly; and on its first introduction it appeared as if 
nothing further could be desired. One of the first and most important 
